U.S. Pat. No. 4,649,884 discloses a fuel delivery system for an internal combustion engine in which an electric-motor constant-delivery fuel pump supplies fuel under pressure from a tank to a fuel rail positioned on an engine. A fuel pressure regulator is connected to the fuel rail to return excess fuel to the supply tank as a function of pressure differential between the fuel rail and the engine air intake manifold, which thus supplies the reference input to the pressure regulator. A plurality of fuel injectors are mounted between the fuel rail and the engine air intake manifold, with the injector nozzles being positioned adjacent to the fuel/air intake ports of the individual engine cylinders.
To overcome a problem of heat transfer from the engine to the fuel tank by the fuel returned from the supply, it has heretofore been proposed to supply fuel to the engine by means of a pressure-controlled electric-motor fuel pump and a one-way or non-return fuel line that connects the pump to the fuel rail at the engine. For example, U.S. Pat. No. 5,044,344 discloses a fuel delivery system in which a fuel pump is responsive to application of electrical power for supplying fuel under pressure from the tank to the fuel rail. A check valve is positioned in the fuel line between the pump outlet and the fuel rail for preventing reverse flow of fuel from the engine to the pump when the pump is shut down. A pressure sensor is operatively coupled to the fuel line between the pump outlet and the check valve, and is connected to electronic circuitry for applying electrical energy to the pump motor as a function of pressure in the fuel line. A pressure relief valve is connected to the fuel line between the check valve and the engine for returning fuel from the engine to the supply in the event of over-pressure in the fuel line.
Although the fuel delivery systems so disclosed address and overcome a number of problems theretofore extant in the art, further improvements remain desirable. For example, placement of a fuel filter in the fuel line between the pump and the engine in a non-return fuel delivery system causes loss of fuel pressure control at the engine as &he filter becomes clogged. Another and continuing problem in the art involves fuel vaporization in the fuel line and at the fuel supply at very high temperatures. For example, fuel rail temperature tends to increase significantly after the engine is turned off and coolant system operation terminates. The fuel may vaporize in the rail and injector area, and at the pump, particularly when ambient temperature is relatively high. Such fuel vaporization typically causes difficulty in restarting the engine and/or unstable idling performance.
It is therefore a general object of the present invention to provide a fuel delivery system for internal combustion engines that includes facility for direct control of fuel pressure at the outlet of the fuel filter so as to maintain substantially constant fuel delivery pressure to the engine as the filter becomes clogged. Another object of the present invention is to provide a fuel delivery system for internal combustion engines in which increasing fuel pressure in the fuel line to the engine under high heat conditions automatically vents the fuel pump so as to reduce vapor formation at the pump. Another object of the present invention is to provide a fuel delivery system that obtains one or both of the aforementioned objectives without use of costly electronic control components and circuitry. A further object of the present invention is to provide a fuel delivery system of the described character in the form of an integral fuel module assembly constructed for immersion in a vehicle fuel tank.